When a copy image is made with a copying machine, it is important that a toner has a fixing strength above a certain level when it is heat-fixed.
When double-surface copying is conducted, in particular, with an automatic double-surface copying machine or with a copying machine equipped with an automatic paper feeder, a scumming due to an insufficient fixing strength of a toner poses a big problem. Further, when a copy image is made on that surface of a copied document which has no copied image with a copy machine equipped with an automatic paper feeder, scumming caused on the reverse surface (which already has a copied image) by insufficient fixing strength of a toner is a big problem.
In order to overcome the above problems, it is conventional practice to use a toner containing a polyethylene-based wax, a natural wax such as carnauba wax, and ethylene-vinyl acetate copolymer, or the like.
In the above prior art toners containing a polyethylene-based wax, a natural wax, or the like, these waxes cause a variety of adverse effects, e.g., the wax unnecessarily adheres to an electrophotographic photoreceptor or a carrier surface to form a film due to defective dispersion of the wax in a binder resin or dissociation of the wax, so-called "filming"; the degree of fogging of a copy caused by the filming increases; and the like.
Further, when a toner contains an ethylene-vinyl acetate copolymer, the preservability of the toner is often liable to be deteriorated due to adhesion properties of the copolymer itself (such a toner powder blocks at a high temperature).